U.S. patent number 5,484,500 [Application Number 08/320,582] was granted by the patent office on 1996-01-16 for method for forming structural panels having a core with thermoplastic resin facings.
This patent grant is currently assigned to E. I. Du Pont de Nemours and Company. Invention is credited to Christine M. Kaufmann, Dale L. Murschell, Dennis A. Nollen, Anthony R. Saracino, Joseph D. Trentacosta.
United States Patent |
5,484,500 |
Kaufmann , et al. |
January 16, 1996 |
Method for forming structural panels having a core with
thermoplastic resin facings
Abstract
A process for fabricating panels of a core material with
thermoplastic resin facings. The core material is either foam or a
honeycomb structure from aramid paper. A belt press machine
provides a means for rapid heating and cooling such that the core
will not degrade. Since the process is so rapid, aramid fibers can
be used to reinforce the resin facings without deleterious
decomposition of the fibers under the temperatures used to heat the
panels during forming.
Inventors: |
Kaufmann; Christine M.
(Boothwyn, PA), Murschell; Dale L. (Woodstown, NJ),
Nollen; Dennis A. (Newark, DE), Saracino; Anthony R.
(Wilmington, DE), Trentacosta; Joseph D. (Wilmington,
DE) |
Assignee: |
E. I. Du Pont de Nemours and
Company (Wilmington, DE)
|
Family
ID: |
24369638 |
Appl.
No.: |
08/320,582 |
Filed: |
October 11, 1994 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
44364 |
Apr 2, 1993 |
|
|
|
|
592179 |
Oct 9, 1990 |
5328744 |
|
|
|
Current U.S.
Class: |
156/198; 156/196;
428/118; 428/117; 428/116; 428/73; 156/583.5; 156/311; 156/309.6;
156/199; 156/289; 156/292 |
Current CPC
Class: |
B32B
27/06 (20130101); B32B 27/10 (20130101); B32B
37/1027 (20130101); B32B 37/06 (20130101); B32B
37/08 (20130101); B32B 27/28 (20130101); B32B
3/12 (20130101); B32B 27/065 (20130101); B32B
5/18 (20130101); B32B 2607/00 (20130101); Y10T
156/1002 (20150115); Y10T 428/31547 (20150401); Y10T
156/1005 (20150115); B32B 2262/106 (20130101); Y10T
428/24165 (20150115); Y10T 428/24149 (20150115); B32B
2262/101 (20130101); B32B 2305/08 (20130101); Y10T
428/24157 (20150115); Y10T 428/236 (20150115); Y10T
428/24777 (20150115); Y10T 156/1007 (20150115); B32B
2262/0269 (20130101) |
Current International
Class: |
B32B
27/06 (20060101); B30B 005/06 (); B32B 031/04 ();
B32B 031/08 (); B32B 031/20 () |
Field of
Search: |
;156/289,292,307.7,311,324,308.2,309.6,583.5,555,196,198-199
;428/116,118,117,73 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Johnstone; Adrienne C.
Parent Case Text
This is a division of application Ser. No. 07/592,179, filed Oct.
9, 1990, now U.S. Pat. No. 5,328,744.
This is a continuation of application Ser. No. 08/044,364 filed
Apr. 2, 1993, now abandoned.
Claims
What is claimed is:
1. A method for bonding a sheet of thermoplastic
polyetherketoneketone resin material to each side of a core member
in the form of a honeycomb structure of aramid paper having a
plurality of adjoining cells formed of walls perpendicular to each
side to form a bonded structure comprising passing the core and
said thermoplastic polyetherketoneketone sheet material in mating
surface contact through a belt press for a residence time period of
less than 2.3 minutes under positive pressure while heating said
core and said thermoplastic polyetherketoneketone sheet material
above the softening point of the core to a temperature of about
650.degree. F. in said belt press whereby said walls are folded at
each side in the direction generally opposite to the direction of
movement of the core to increase the surface area of the honeycomb
structure contacting said thermoplastic polyetherketoneketone resin
material; and cooling said core and said sheet material in said
belt press while maintaining said positive pressure.
2. The method of claim 1 wherein said positive pressure is from
about 4 psi to about 300 psi.
3. The method of claim 1 wherein said sheet of thermoplastic
polyethericetone ketone resin material is reinforced with fiber.
Description
BACKGROUND OF THE INVENTION
This invention relates to a method for rapidly forming structural
panels having a core faced with thermoplastic resin facings.
In the manufacture of composite panels with resin facing material
bonded to core structures, it has been the practice to use facing
materials made with thermosetting resins which are cured as the
panel is consolidated in an autoclave, oven or press which is a
costly and a time-consuming operation. Attempts to use high
performance thermoplastic resin sheet material as facings for these
panels require higher processing temperatures than thermoset
resins. This leads to decomposition of core materials and to panels
with low adhesion between the facings and the core material when
the facings are resin reinforced with fibers.
SUMMARY OF THE INVENTION
According to the method of this invention, a composite structure is
formed from a core and a thermoplastic resin sheet material by
bonding the thermoplastic resin sheet material to at least one side
of the core by passing the core and the thermoplastic resin sheet
material in mating surface contact through a belt press for a
residence time of less than 2.3 min. under a positive pressure such
as a positive pressure in the range of about 4 psi to about 300
psi, while heating the core and the thermoplastic sheet material to
a temperature of from about 480.degree. F. to about 710.degree. F.,
for example about 650.degree. F., in the belt press and cooling the
core and the sheet material in the belt press while maintaining
said positive pressure. The residence time and process temperature
are adjusted to give optimum resin impregnation while minimizing
core or organic fiber facing reinforcement degradation.
Another embodiment of the invention is a panel formed by the above
method that includes a core member and a fiber reinforced
thermoplastic resin sheet material bonded to at least one side of
the core member to form a facing therefor. The thermoplastic resin
is between 30 to about 65 weight percent of the facing. The peel
strength or adhesion between the facing and the core is greater
than 10 lbs./3" sample.
Useful cores are honeycomb structures of aramid paper, aluminum or
glass fibers and foams such as polymethacrylimide and
polyetherimide foams or polyurethanes and polyisocyanurate
foams.
Suitable thermoplastic resins include polyesters, polyamides,
copolyamides polyolefins and polyetherketoneketone (PEKK) both
amorphous and semicrystalline. The polyaryletherketone resin
consists of repeating units (as disclosed in U.S. Pat. No.
4,937,135) of 1,4 phenylene groups (T, terephhalyl groups) and 1,3
phenylene groups (I, isophthalyl groups); the T:I ratio being 50:50
to 80:20, preferably 60:40 to 70:30. Polyetheretherketone (PEEK)
Stabar.TM. from ICI, polyetherimide (PEI) Ultem.TM. from GE, and
polyethersulfone (PES) Radel.TM. X from Amoco. The ratio of resin
to reinforcement can vary. Such properties as peel strength
increase linearly with increasing resin content. However, extra
resin adds weight to the finished panel which is undesirable in
aerospace applications. The preferred resin contents are similar to
the corresponding thermoset values for self-bonding prepregs, i.e.
about 50% by weight for reinforcement with fabrics of Kevlar.TM.
aramid fibers, about 45% by weight for woven carbon fiber facings
and about 40% by weight for fiberglass facings. For panels with
maximum bending stiffness, the thermoplastic resin and fiber
reinforcement may be consolidated in a separate step under high
pressure before bonding to the core in the method described
above.
Useful fibers for reinforcing the thermoplastic resin facings are
carbon, aramid and glass fibers.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic side view of a belt press suitable for
practicing the method of this invention.
FIG. 1A is a schematic side view of a batch mode operation.
FIG. 2 is a schematic side view of a continuous mode operation.
FIG. 3 is a schematic side view showing a honeycomb core and
facings entering the nip of a belt press.
FIG. 4 is a photomicrograph of a partial elevation view in cross
section of a panel formed with a honeycomb core of aramid
paper.
FIG. 5 is a schematic side view showing a foam core and facings
entering the nip of a belt press.
FIGS. 6 and 7 are schematic illustrations of a partial elevation
view in cross section of a panel formed with foam cores of
thermoplastic and non-thermoplastic foam, respectively.
FIG. 8 is a schematic illustration plan view of a panel having a
form edge trim for a honeycomb core.
FIG. 9 is a section of FIG. 8 taken along the line 9--9.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1 the belt press has been designated generally by the
numeral 10 and shown to include substantially identical upper and
lower sections 12 and 14, respectively, that are aligned one above
the other. Each section includes a pair of belt rolls 11, 13 on the
upper and 15', 17 on the lower. The rolls are rotatably mounted to
frame (not shown). Traveling around rolls 11, 13 is a metal alloy
belt 18 and around rolls 15 and 17 an identical belt 20. Both belts
coact to form a constant height nip section within the frame
hereafter referred to as the heating and cooling zone 22. Each belt
is supported on its back side in the zone 22 by a stationary
antifriction bearing 24 sandwiched between the stationary zone and
the moving belts. Belt tension rolls 28, 30 are mounted for
rotatable and vertical movement as indicated by the direction
arrows. The belts are driven in the direction of the arrows by
conventional drive means (not shown). Each zone 22 is composed of
heating sections 32, 34, and cooling sections 36 separated by
thermal barriers 38. The zones are attached to the frame with
mechanical shims 26, 26a in a fashion to allow vertical positioning
for maintaining a constant spacing between the belts.
There are numerous heating and cooling concepts practiced by
commercial belt press suppliers. Heating systems use an electrical
heat source to generate heat and then carry the heat to the belt
via pneumatic, hydraulic and regular conduction techniques. The
source of cooling is usually a water supply with the heat being
carried from the belt by pneumatic, hydraulic and conductive
systems.
In order to provide capability for the belt press to operate at
temperatures above 540.degree. F. the static anti friction bearings
24 of woven screen must be permanently impregnated with either a
dried graphite paste, a dried molylube N(molybdenum) paste or a
graphite sheeting, which are all high temperature and low
volatility substrates which fill the voids in the screen. The
bearing surface must then be coated periodically with a high
temperature and low volatility lubricant such as C5A (Fel Pro,
Inc., Skokie, Ill.), a copper based lubricant, Molylube-16 (Bel-Ray
Co., Inc., Farmingdale, NJ), a molybdenum based lubricant, or
Krytox.TM. paste (Du Pont), a fluorinated lubricant.
In a batch mode of operation shown in FIG. 1A, a Dayup consisting
of a core member 50 and facings 50a comprised either of
preimpregnated fiber reinforced sheets or sheets of thermoplastic
resin and fabrics of high performance fibers (glass, aramids or
carbon) is introduced from platform 49 into the nip between the
belts 18 and 20. If necessary, a release film 52 is unrolled from
the supply roll 51 to cover belts 18 and 20. The facings are bonded
to the core as the layup passes through zone 22 of FIG. 1 under a
positive pressure created by the difference in the opening between
the belts and the thickness of the core and its facings. Usually
the bonding pressure is limited by the compressive strength of the
core at the processing temperature. A stationary platen press of
the type known to one skilled in the art could also be used to heat
and bond the facing 50 to the core 50.
While FIG. 1A shows a system set up for a batch mode of operation,
it is to be understood that a (single step) continuous mode of
operation could be obtained as disclosed in FIG. 2 wherein a
continuous core 50' is fed to the nip of the belt press 10 from
platform 49. Upper and lower facings 60, 62, respectively, are
formed from a reinforcing fabric 64, sandwiched between
thermoplastic resin sheets 66, 68 (in the case of upper facing 60)
and 64a sandwiched between thermoplastic resin sheets 65, 67 (in
the case of lower facing 62) a release film 70 such as Kapton.TM.
(polyimide film) is fed between the upper and lower facings and the
belts of the belt press 10, Kapton.TM. (fluoropolymer resin) ,
aluminum or Teflon.TM. coated glass fabric are needed for a release
agent with certain thermoplastic sheets but may not be required by
others. The panels are formed in the belt press in substantially
the same manner as described above except the operation is
continuous.
Panels made according to the above procedure are then tested for
damage tolerance via the climbing drum peel test (ASTM D781-76;
reapproved 1986). Panels exhibiting at least 10 pounds of peel per
3" sample have sufficient damage tolerance for use in aircraft
interiors. If higher peel strengths are desired with honeycomb of
Nomex.TM. (aramid paper), crushed-core panels can be made. With the
above technology, peel strengths can be enhanced by as much as 3-4
times versus noncrushed core panels. This is because the bonding
surface area has been increased. More particularly, as shown in
FIG. 3, a honeycomb core member 50" is introduced into the nip
between belts 18, 20 along with fiber reinforced resin facings 52.
As they pass through the nip under positive pressure, the cell
walls of the honeycomb structure are folded into hooklike
configurations pointed generally in a direction opposite to the
direction of movement of the core, thus increasing the surface area
of the honeycomb structure contacting the facings 52'. With the new
thermoplastic facing technology, the core is heated above its
softening point such that the cells are crushed much more uniformly
than with conventional thermoset crushed-core panels which have
considerable cell damage after panel fabrication leading to a
decrease in certain physical properties such as bending stiffness.
An alternate embodiment using a foam core is shown in FIG. 5
wherein a foam core member 50" is introduced into the nip between
belts 18 and 20 along with fiber reinforced resin facings 52".
If the foam is thermoplastic in nature, as shown in FIG. 6, a
strong bond 54 is formed between the foam and the facing resin as
defined by peel strength exceeding 30 lbs./3" width. This strong
bond results from fusion bonding (i.e. melting together of the
facing resin and the melted foam surface) between the resin and the
foam at the interface. The heat from the belt press melts the
surface of the foam as seen by thickening of the foam cell walls
near the interface. The heat is not applied long enough to
penetrate through the thickness of the foam, therefore, the foam
interior remains intact. Examples of foams which will bond to
thermoplastic PEKK resin in this manner are polymethacrylimide
foams (Rohacell.TM.) and polyetherimide foams (Airex.TM.).
If the foam is not thermoplastic in nature, as shown in FIG. 7, a
strong bond 54' is formed between the foam and facing resin which
results from flow of the PEKK polymer into the cells at the
interface, resulting in a bond of increased surface area at the
interface. The resin flows into and around the surface cell walls
of the foam core. The strong bond is characterized by peel strength
of greater than 25 lbs./3" width. Examples of foams which will bond
to PEKK resin in this manner are polyurethanes and
polyisocyanurates (Last-A-Foam.TM.).
In addition to being used as core materials, these foam materials
have been demonstrated for use as an edge trim to honeycomb cored
sandwich panels as shown in FIGS. 8 and 9. The foam edge trim
member acts as a barrier to moisture for the honeycomb, as a
location for fastener attachment, and also as a smooth edge finish
for an aircraft part. The foam edge 50" is held in place around the
honeycomb core member 50" for processing by a variety of methods.
In the preferred method a screw 56 is used to mechanically fasten
the foam strips together at each splice point. Other types of
fasteners at the splice point which have been demonstrated include
Kapton.TM. tape or fast drying adhesives. Ultrasonic bonding of the
face sheets to the core or a wooden frame around the edges of the
panel have been demonstrated as techniques to hold the foam in
place without fasteners.
EXAMPLES
Example 1
The components of the laminate were dried for at least 2 hours at
120.degree. C. and then laid up in the following manner. Three
pieces of amorphous (60/40 T/I) PEKK film (1.5 mils thick, 150 melt
index as measured by ASTM 1238-79 procedures) were placed on the
core bonding side of Kevlar.TM. 49 aramid fiber (by Du Pont) Style
285 fabric (5.1 oz./sq. yd., 9 mils thick) and one piece on the
belt contact side to form the top facing. The bottom facing
consisted of a balanced 2 pieces of film on each side of the
Kevlar.TM. (aramid fiber) The resin percentage by weight of the
facings was 54%. The facings were placed on each side of a piece of
honeycomb of Nomex.TM. aramid paper (by Du Pont) (3 lbs./cu. ft.,
1/8" cell, 1/2" thick). The warp direction of the .fabric was
aligned with the ribbon direction of the core. The warp face of the
fabric was placed against the core. The facing layers were anchored
to the core material with two 1" wide Kapton.TM. tape strips along
the leading edge of the sample. The belt press (substantially as
shown in FIG. 2) was set to a constant temperature of 650.degree.
F. and a belt speed of 15" per min. (approximately 32 sec.
residence time in the heat zone). The gap between the upper and
lower belts was fixed to give a panel thickness of 0.518". A
Kapton.TM. polyimide release sheet (by Du Pont) was placed over
both sides of the entire laminate. The front edge of the sample,
perpendicular to the warp direction of the facing fabric and
containing the Kapton.TM. tape anchors, was inserted into the belt
press. Once consolidated, the Kapton.TM. release film and tape
anchors were removed from the sample.
The panel was cut into three 3".times.12" samples (length
perpendicular to the warp direction). Peeling the 3 ply
PEKK/Kevlar.TM. ply PEKK facing from the core gave an average peel
strength of 28.4 lbs./3" sample.
Example 2
The components of the laminate were dried for at least 2 hours at
120.degree. C. and then laid up in the following manner. Two pieces
of amorphous (60/40 T/I) PEKK film (1.5 mils thick, 150 melt index
as measured by ASTM 1238-79 procedures) were placed on each side of
Style 7781 glass (9 mils thick). The facesheet was consolidated at
belt press conditions of 650.degree. F. and 15"/min. belt speed
(about 32 sec. in the heating zone). The gap between upper and
lower belts was adjusted to give a sample thickness of 0.012". A
second facesheet was consolidated in an identical fashion. The
resin percentage by weight of the facings was 39%. The described
facings were then placed on each side of a piece of honeycomb of
Nomex.TM. (3 lbs./cu. ft., 1/8" cell, 1/2" thick). The facings were
anchored to the core material with two 1" wide Kapton.TM. tape
strips along the leading edge of the sample. The belt press was set
to a constant temperature of 625.degree. F. and a belt speed of 15"
per min. (residence time approximately 32 sec. in the heat zone).
The gap between the upper and lower belts was fixed to give a
sample thickness of 0.516". A Kapton.TM. release sheet was placed
over both sides of the entire laminate. The front edge of the
sample, perpendicular to the warp direction of the facing fabric
and containing the Kapton.TM. tape anchors, was inserted into the
belt press. The belt press conditions were then adjusted to a
constant 500.degree. F. and 3.5"/min. (residence time about 2.3
min. in the heat zone) belt speed and the panel was inserted as
before. Once consolidated, the Kapton.TM. release film and tape
anchors were removed from the sample.
The panel was cut into three 3" by 8" samples (length parallel to
the core ribbon direction) The specimens gave an average short beam
shear value of 100 psi.
Example 3
The components of the laminate were dried for at least 2 hours at
120.degree. C. and then laid up in the following manner. Two pieces
of amorphous (60/40 T/I) PEKK film (1.5 mils thick, 180 melt index)
were placed on each side of a Kevlar.TM. Style 281 fabric, 5.1
oz./sq. yd., 10 mils thick, to form the facing To achieve a sample
size of 14".times.17" 6.5" strips of the above mentioned amorphous
PEKK film were concurrently placed over a 14".times.17" piece of
core material being careful not to overlap film edges. Identical
facings were placed on each side of a piece of honeycomb of
Nomex.TM. (3 lbs./cu. ft., 1/8" cell, 1/2" thick). The warp
direction of the fabric was aligned with the ribbon direction of
the core. The facing layers were anchored to the core material with
two 241 wide Kapton.TM. tape strips along the leading edge of the
sample. The belt press was set to a constant temperature of
650.degree. F. and a bolt speed of 12" per min. (residence time
approximately 48 sec. in the heat zone). The gap between the upper
and lower belts was set to achieve a total sample thickness of
0.36" (70% of the theoretical thickness). A Kapton.TM. release
sheet was placed over both sides of the entire laminate according
to the above described procedure. The front edge of the sample,
perpendicular to the warp direction of the facing fabric and
containing the Kapton.TM. tape anchors, was inserted into the belt
press. The Kapton.TM. release film and the tape anchors were
removed from the sample. The average sample thickness, as measured
by a micrometer, was found to be 0.387". Three 3".times.12" samples
(long direction perpendicular to the warp direction) were cut from
the sample. The average peel strength was determined to be 56
lbs./3" sample.
Example 4
The components of the laminate were dried for at least 2 hours at
120.degree. C. and then laid up in the following manner. Two pieces
of polyethermide Ultem.TM. film were placed on each side of a
Kevlar.TM. Style 281 fabric, 5.1 oz./sq. yd., 10 mils thick, to
form the facing. Identical facings were placed on each side of a
piece of honeycomb of Nomex.TM. (3 lbs./cu. ft., 1/8" cell, 1/2"
thick). The warp direction of the facing fabric was aligned with
the ribbon direction of the core. The facing layers were anchored
to the core material with two 1" wide Kapton.TM. tape strips along
the leading edge of the sample. The belt press was set to a
constant temperature of 650.degree. F. and a belt speed of 15"/min.
(residence time about 32 sec. in the heat zone). The gap between
the upper and lower belts was set to achieve a total sample
thickness of 0.44" (85% theoretical gap). A Kapton.TM. release
sheet was placed over both sides of the entire laminate according
to the above described procedure. The front edge of the sample,
perpendicular to the warp direction of the facing fabric and
containing the Kapton.TM. tape anchors, was inserted to the belt
press. The Kapton.TM. release film and the tape anchors were
removed from the sample. A Climbing Drum Peel test was performed on
three samples and had an average result of 11.0 lbs./3" sample.
Example 5
The components of the laminate were dried for at least 2 hours at
120.degree. C. and then laid up in the following manner. Two pieces
of 70/30 T/I, PEKK film were placed on the top side of a Kevlar.TM.
49 Style 281 fabric (5.1 oz./sq. yd., 10 mils thick) and two pieces
of 60/40 T/I PEKK film (180 melt index as measured by ASTM 1238-79)
on the bottom to form the facing. The percentage of resin by weight
was about 49. Identical facings were placed on each side of a piece
of honeycomb of Nomex.TM. (3 lbs./cu. ft., 1/8" cell, 1/2" thick).
The 60/40 T/I film was placed next to the honeycomb core on both
sides. To achieve a sample size of 13".times.17" 6.5", strips of
the above mentioned amorphous PEKK films were concurrently placed
over a 14".times.17" piece of the core material being careful not
to overlap film edges. The warp direction of the fabric was aligned
with the ribbon direction of the core. The facing layers were
anchored to the core material with two 1" wide Kapton.TM. tape
strips along the leading edge of the sample. The belt press was set
to a constant temperature of 650.degree. F. and a belt speed of
15"/min. (residence time approximately 32 sec. in the heat zone).
The gap between the upper and lower belts was fixed to 0.360" (70%
theoretical thickness). A Kapton.TM. release sheet was placed over
both sides of the entire laminate. The front edge of the sample,
perpendicular to the warp,direction of the facing fabric: and
containing the Kapton.TM. tape anchors, was inserted into the belt
press. Once consolidated the Kapton.TM. release film and tape
anchors were removed from the sample. The average sample thickness,
as measured by a micrometer, was found to be 0.365".
Three 3".times.12" samples (length perpendicular to the warp
direction) were cut from the sample. The peel strength was
determined to be 27 lbs./3" sample.
Example 6
The components of the panel were dried for at least 2 hours at
120.degree. C. and then laid up in the following manner. Three
pieces of amorphous polyetheretherketone (PEEK) film (Stabar
K200-782), 1.06 oz./sq. yd., melt index @360.degree. C. as measured
by ASTM 1238-79 procedures, were laid over a piece of 1/2" thick
Nomex.TM. honeycomb core. Then a piece of 7781 glass fabric was
placed atop the film layers with the warp direction of the fabric
parallel to the core ribbon direction and the warp face towards the
core. Three more layers of film were then placed on the fabric.
This layup was intended to produce a resin content on the face
sheets of approximately 41%. The film and fabric stacked layup was
duplicated on the reverse side of the core. The layers of film and
fabric were anchored to the core by ultrasonic welder along the
leading edge of the panel. The belt press was set to a constant
temperature of 680.degree. F. and a belt speed of 15" per min.
(about 32 sec. residence time in the heat zone). The gap between
the belts was adjusted to give a product thickness of 44", or 85%
of the theoretical thickness expected. A Kapton.TM. release sheet
was placed over both of the entire laminate. The laminate was
placed into the belt press such that the ribbon direction of the
core was parallel to the machine direction, with the edge that had
been ultrasonic spot welded entering the belt press first. After
consolidation, the release sheets were removed from the surfaces of
the laminate.
Three 3".times.12" samples were cut from the panel, length
perpendicular to the core ribbon direction. The average peel
strength of the three samples was found to be 15 lbs./3"
sample.
Example 7
The components of the laminate were dried for at least 2 hours at
120.degree. C. and then laid up in the following manner. Two pieces
of amorphous (60/40 T/I) PEKK film (130 melt index as measured by
ASTM 1238-79 procedures) were placed on each side of a Kevlar.TM.
49 Style 281 fabric, 5.1 oz./sq. yd., 10 mils thick, to form the
facing. The percentage of resin by weight was calculated to be 51%.
Identical facings were placed on each side of a piece of honeycomb
of aluminum (3 lbs./cu. ft., 1/8" cell, 1/2" thick). To achieve a
sample size of 13".times.17" 6 5", strips of the above mentioned
amorphous PEKK film were concurrently placed over a 14".times.17"
piece of the core material being careful not to overlap film edges.
The warp direction of the fabric was aligned with the ribbon
direction of the core. The facing layers were anchored to the core
material with two 1" wide Kapton.TM. tape strips along the leading
edge of the sample. The belt press was set to a constant
temperature of 650.degree. F. and a belt speed of 15"/min.
(residence time approximately 32 sec. in the heat zone). The gap
between the upper and lower belts was fixed to give a sample
thickness of 0.516". A Kapton.TM. release sheet was placed over
both sides of the entire laminate. The front edge of the sample,
perpendicular to the warp direction of the facing fabric and
containing the Kapton.TM. tape anchors, was inserted into the belt
press. Once consolidated the Kapton.TM. release film and tape
anchors were removed from the sample. The average sample thickness,
as measured by a micrometer, was found to be 0.523".
Three 3".times.12" samples (length perpendicular to the warp
direction) were cut from the sample. The peel strength was
determined to be 11.9 lbs./3" sample.
Example 8
The components of the laminate were dried for at least 2 hours at
120.degree. C. and then laid up in the following manner. Two pieces
of amorphous (60/40 T/I) PEKK film (150 melt index) were placed on
either side of a Kevlar.TM. Style 281 fabric, 5.1 oz./sq. yd., 10
mils thick, to form the panel facings. One inch wide strips of 1/2"
thick foam (Last-A-Foam.TM. FR-10118 polyisocyanurate by General
Plastics Mfg. Co., Tacoma, Wash.) were cut from a sheet of foam and
assembled into a frame with outer dimensions measuring
12".times.16". The strips of foam were held together using a rigid
wooden frame with inner dimensions of 12".times.16". A piece of
Nomex.TM. honeycomb core cut exactly to 10".times.14" was fitted
into the center of the frame. The identical facings described above
were then placed on each side of the foam-framed Nomex.TM.
honeycomb such that the warp direction of the fabric ran in the
ribbon direction of the honeycomb core. One inch wide strips of
Kapton.TM. tape were used to anchor the facings to the frame along
the leading edge of the sample. The belt press was set to a
constant temperature of 650.degree. F. with a belt speed of
15"/min. (residence time approximately 32 secs. in the heat zone).
The gap between the upper and lower belts was set to produce a
finished sample thickness of 0.516" or 100% of the theoretical
thickness. The front edge of the sample with the Kapton.TM. tape
anchors) was inserted into the belt press. This sample was covered
with Kapton.TM. film as a release agent to prevent the sample from
sticking to the belts. Once consolidated the Kapton.TM. release
film and tape anchors were removed from the sample. The finished
panel edges were trimmed, leaving 1/2" width of foam around the
panel. The average thickness of the foam trimmed portion of the
panel, as measured by a micrometer, was 0.507" and the average
thickness of the honeycomb cored portion of the sample was measured
to be 0.494".
Example 9
The components of the laminate were dried for at least 2 hours at
120.degree. C. and then laid up in the following manner. Identical
panel facings as described in Example 8 were laid up 1.5" strips of
1/2" thick foam (Rohacell.TM. 200 WF polymethacrylimide by Rohm
Tech, Inc., Malden, Mass.) were cut from a foam sheet and assembled
into a frame with outer dimensions measuring 12".times.12". The
strips of foam were anchored together using Kapton.TM. tape. A
piece of Nomex.TM. honeycomb core cut exactly to 9".times."
"dimensions was fitted into the center of the frame. The identical
facings were placed on either side of the foam-framed Nomex.TM.
honeycomb with the warp direction of the fabric parallel to the
ribbon direction of the honeycomb core. The Kapton.TM. tape was
used to anchor the facings in place along the leading edge of the
sample. The belt press was set to a constant temperature of
650.degree. F. with a belt speed of 15"/min. (residence time about
32 sec. in the heat zone). The gap between the upper and lower
belts was set to produce a finished sample thickness of 0.516". The
panel was then consolidated in the belt press using Kapton.TM.
release film. After processing, the Kapton.TM. film and tape were
removed. This sample was then reprocessed to apply a decorative
laminate to one side of the panel. The belt press was set to a
constant temperature of 250.degree. F. and 6"/min. (residence time
about 80 sec. in the heat zone). The panel was consolidated using
Kapton.TM. release film which was removed after processing. The
finished average thickness of the foam was measured to be 0.521"
and the honeycomb core thickness was 0.516".
Example 10
The components of the laminate were dried for at least 2 hours at
120.degree. C. and then laid up in the following manner. Two pieces
of amorphous (60/40 T/I) PEKK film (150 melt index) were placed on
either side of a Kevlar.TM. Style 281 fabric, 5.1 oz./sq. yd., 10
mils thick, to form the panel facings. Dimensions of the fabric and
film measured 16".times.25". A piece of foam core (Rohacell.TM. 200
WF, polymethacrylimide) was cut to these same dimensions. The
facings were placed on either side of the foam and anchored in
place using two 1" wide Kapton.TM. tape anchors along the leading
edge of the sample. The warp direction of the fabric was aligned
along the length (25") direction of the panel. The belt press was
set to a constant temperature of 650.degree. F. with a belt speed
of 15"/min. (residence time about 32 sec. in the heat zone). The
gap between the upper and lower belts was set to produce a finished
sample thickness of 0.516" or 100% of the theoretical thickness.
The leading edge of the sample was inserted into the belt press. A
Kapton.TM. release film was used when processing the sample. After
consolidation the release film and tape anchors were removed. The
average sample thickness, as measured by the micrometer, was
0.540".
This panel was cut into five 3".times.24" strips for long beam flex
evaluation as described in test Boeing Mil. Spec. 256, page 29. The
average flex strength was determined to be 14.7 ksi at maximum
machine deflection. An identical sample was manufactured but with
the warp direction of the fabric perpendicular to the length of the
foam cored panel. This sample was cut into 3".times.12" samples for
climbing drum peel evaluation. The average peel strength was
determined to be 33 lbs. per 3" sample.
Example 11
The components of the laminate were dried for at least 2 hours at
120.degree. C. and then laid up in the following manner. Identical
facings as described in Example 9 were placed on each side of a
piece of foam (Last-A-Foam.TM. FR 3718 polyurethane) measuring
16".times.25" with the warp direction of the fabric parallel to the
length of the panel. Two Kapton.TM. tape strips were used to anchor
the facings to the core along the leading edge of the panel. The
panel was consolidated using a constant belt press temperature of
600.degree. F. and a constant belt speed of 12"/min. (residence
time about 48 sec. in the heat zone). Kapton.TM. release film was
used during consolidation. After consolidation the release film and
tape anchors were removed. The average panel thickness was measured
to be 0.541".
This panel was cut into samples for long beam flex evaluation. The
average flex strength was determined to be 13 ksi at maximum
machine deflection. An identical sample was manufactured with the
warp direction perpendicular to the length of the panel for
climbing drum peel evaluation. Manufacturing conditions for this
sample were 650.degree. F. belt temperature and 15"/min. belt speed
(residence time about 32 sec. in the heat zone). The average peel
strength was determined to be 27 lbs./3" sample.
Example 12
The components of the laminate were dried for at least 2 hours at
120.degree. C. and then laid up in the following manner. Identical
facings of amorphous (60/40) PEKK film and Kevlar.TM. fabric Style
281 were placed on either side of a foam (Last-A-Foam.TM. FR 10118
polyisocyanurate) core. Two 1" wide strips of Kapton.TM. were used
to anchor the facings in place along the leading edge of the
sample. All parts of the lay-up were cut to dimensions of
12".times.16". The warp direction of the was laid parallel to the
length of the panel. The panel was consolidated using a constant
belt press temperature of 650.degree. F. and a constant belt speed
of 12"/min. (residence time about 48 sec. in the heat zone). The
gap between the upper and lower belts was set to achieve a finished
panel thickness of 0.516". The Kapton.TM. release film was used
during panel processing. After consolidation the Kapton.TM. film
and tape were removed. The panel was cut into four 3".times.12"
samples with the warp direction of the fabric parallel to the 3"
dimension. The average peel strength of this panel by the climbing
drum peel strength test method was determined to be 27 lbs./3"
sample.
Example 13
The components of the laminate were dried for at least 2 hours at
120.degree. C. and then laid up in the following manner. One piece
of amorphous nylon film (0.008" thick) was placed on each side of a
flat woven 5.times.5 harness satin fabric (15 oz./sq. yd. code,
T5674-34) made from E-glass/amorphous nylon impregnated tow
(Binnersley and Krueger U.S. Pat. No. 4,640,861) to form the
facing. Identical facings were placed on each side of a piece of
honeycomb of Nomex.TM. (3 lbs./sq. ft., 1/8" cell, 1/2" thick). The
warp direction of the facing fabric was aligned with the ribbon
direction of the core and the predominantly warp faced side of the
fabric placed closest to the core. The facing layers were anchored
to the core with (3) 1" wide Kapton.TM. tape strips along the
leading edge of the sample. The belt press was set to a constant
temperature of 650.degree. F. and a belt speed of 15"/min.
(residence time about 32 sec. in the heat zone). The gap between
the upper and lower belts was set to achieve a total sample
thickness of 0.504". A Kapton.TM. release sheet was placed over
both sides of the entire laminate according to the above described
procedure. The front edge of the sample, perpendicular to the warp
direction of the facing fabric and containing the Kapton.TM. tape
anchors, was inserted into the belt press. The Kapton release sheet
and the tape anchors were removed from the sample. The average
sample thickness, as measured by micrometer, was found to be
0.507". A Climbing Drum Peel test was performed on three samples
(in the fabric warp direction) and had an average result of 19.1
lbs./3" sample.
Example 14
The components of this panel were dried for at least 2 hours at
120.degree. C. and then laid up in the following manner. A piece of
amorphous PEKK (60/40) film (Melt index 150) was laid over a piece
of 1/2" Nomex.TM. honeycomb core. A piece of PEEK/AS4 unit tape
(ICI Fiberite APC-2/AS-4 12" unit tape, batch No. N89-0038, roll
No. 11) was then placed upon the core with the fibers in the tape
running perpendicular to the ribbon direction of the core. Another
piece of the same tape was then placed on the stack, but with the
AS-4 fibers running parallel to the ribbon direction of the core.
The tape layup was repeated in the same fashion for the opposite
side of the core, including the layer of PEKK film. The facing
layers were fastened to the core material with Kapton.TM. tape
along the leading edge of the sample for insertion into the belt
press (an edge perpendicular to the ribbon direction of the core).
The belt press was set up for a constant temperature of 680.degree.
F. and a belt speed of 15"/min. (residence time about 32 secs. in
the heat zone). The gap between the upper and lower belts was fixed
to a final sample thickness of 0.516". A Kapton.TM. release sheet
was placed over both sides of the entire laminate. The leading edge
of the layup was inserted into the belt press. Once consolidated,
the Kapton.TM. release film and the Kapton.TM. tape were removed
from the sample. The average sample thickness as measured by
micrometer was found to be 0.512".
The completed panel was then cut into three 3".times.24" specimens
(length parallel to the 25 ribbon direction of the core) and tested
for flexural strength and modulus according to method BMS-256.
Test results:
Long Beam Flex
Modulus - Average 174
Strength - 27754 psi
Another sample was fabricated in the above manner except that the
facing ply orientation of the unit graphite tape was reversed to
give maximum peel strength. Therefore, the 0.degree. axis of the
fibers was placed parallel to the ribbon direction of the honeycomb
core and the outer ply was placed perpendicular to the core ribbon
direction. Peel strength samples were then cut in a perpendicular
orientation to the core ribbon direction. The measured peel value
was determined to be 13.6 lbs./3" sample.
Example 15
The components of the laminate were laid up in the following
manner. Two strips of foam measuring 17.5".times.2" and two strips
measuring 8".times.2" were cut from a sheet of Rohacell.TM.(rigid
plastic foam) 200WF foam. These foam strips were assembled into a
frame 17.5" long and 12" wide held together with 2.5" regular
screws inserted into the side approximately 1/2" from the panel
edge. A piece of honeycomb was cut to fit tightly into the center
of the frame. Identical panel facings composed of two pieces of
amorphous (60/40 T/I) PEKK film (150 melt index) on either side of
a Kevlar.TM. Style 285 fabric were assembled and placed on either
side of the honeycomb core/foam frame assembly. One inch wide
strips of Kapton.TM. tape were used to anchor the panel facings in
place along the leading edge of the sample. The belt press was set
to a constant temperature of 650.degree. F. with a belt speed of
15"/min. Sample-residence time in the heat zone was approximately
32 secs. The gap between the upper and lower belts was set to
produce a finished sample thickness of 0.516" or 100% of the
theoretical thickness. The sample was inserted into the belt
process with Kapton.TM. film as the release agent. After
consolidation, the release film and tape anchors were removed
visual inspection of the panel surface indicates that minimal space
exists at the foam/honeycomb interface. The finished average
thickness of the foam trimmed portion of the panel, as measured by
a micrometer, was 0.539", and the average thickness of the
honeycomb-cored portion of the sample was measured as 0.536".
* * * * *